[time-nuts] 10811 warmup (Jason Rabel)

[Jason Rabel]

Thanks Bruce,

I think we have gotten a little off-subject here... My issue is not with the
oven, but the oscillator circuit itself. I'm not getting any signal on pin
1.

I removed the assembly from the insulation easy enough, I haven't gotten any
further yet, been troubleshooting my shera board today. I don't hear
anything rattling inside so I don't think the crystal is physically broken
like Chris mentioned. 

Jason



-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Dr Bruce Griffiths
Sent: Sunday, January 21, 2007 3:28 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 10811 warmup (Jason Rabel)

Jason

As long as the thermistor is still within the oven mass and the 
temperature regulation circuit is functioning OK, the oven should 
actually be OK.
However the temperature control loop may oscillate as the thermal time 
constant for which it has been compensated has been drastically 
decreased by removing the insulation from the oven mass.
If the oscillation amplitude is sufficient it is conceivable that some 
damage due to excessive temperature may occur.
However, the dissipation of the oven heater transistors is limited by 
the control circuit so the temperatures reached may not be high enough 
to damage components.
The turn on current limit circuit limits the heater transistor emitter 
current to about 0.52A with a 24V heater supply, limiting the maximum 
dissipation in the heater transistors to about 12.5W with a 24V heater 
supply, which is probably insufficient for the inner oven mass to get 
very hot once the insulation is removed.
The principal problem is personal burn injury .

Bruce